package com.example.week07.utils;

/**
 * 基于Twitter_Snowflake的id生成器
 *
 * @author wuwnlong
 */
public class IdGenerateUtil {

    /**
     * ID生成器
     */
    private static IdGenerate generate;

    /**
     * 设置id生成器
     *
     * @param idGenerate
     */
    public static synchronized void setGenerate(IdGenerate idGenerate) {
        if (generate == null) {
            generate = idGenerate;
        }
    }

    /**
     * 生成一个id
     *
     * @return
     */
    public static long genId() {
        if (generate == null) {
            generate = new IdGenerate();
        }
        return generate.nextId();
    }

    public static String genIdToStr() {
        return String.valueOf(genId());
    }

    /**
     * id生成器
     */
    public static class IdGenerate {

        /**
         * 开始时间截 (2015-01-01)
         */
        private final long twepoch = 1420041600000L;

        /**
         * 机器id所占的位数
         */
        private final long workerIdBits = 5L;

        /**
         * 数据标识id所占的位数
         */
        private final long datacenterIdBits = 5L;

        /**
         * 支持的最大机器id
         */
        private final long maxWorkerId = 63L;

        /**
         * 支持的最大数据标识id
         */
        private final long maxDatacenterId = 63L;

        /**
         * 序列在id中占的位数
         */
        private final long sequenceBits = 12L;

        /**
         * 机器ID向左移12位
         */
        private final long workerIdShift = sequenceBits;

        /**
         * 数据标识id向左移位数
         */
        private final long dataCenterIdShift = sequenceBits + workerIdBits;

        /**
         * 时间截向左移位数
         */
        private final long timestampLeftShift = sequenceBits + workerIdBits
                + datacenterIdBits;

        /**
         * 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095)
         */
        private final long sequenceMask = 4095L;

        /**
         * 工作机器ID(0~31)
         */
        private long workerId;

        /**
         * 数据中心ID(0~31)
         */
        private long dataCenterId;

        /**
         * 毫秒内序列(0~4095)
         */
        private long sequence = 0L;

        /**
         * 上次生成ID的时间截
         */
        private long lastTimestamp = -1L;

        /**
         * 构造函数
         *
         * @param workerId     工作ID
         * @param dataCenterId 数据中心ID
         */
        public IdGenerate(long workerId, long dataCenterId) {
            if (workerId > maxWorkerId || workerId < 0) {
                throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
            }
            if (dataCenterId > maxDatacenterId || dataCenterId < 0) {
                throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
            }
            this.workerId = workerId;
            this.dataCenterId = dataCenterId;
        }

        public IdGenerate() {
            this.workerId = 0L;
            this.dataCenterId = 0L;
        }


        /**
         * 获得下一个ID (该方法是线程安全的)
         *
         * @return SnowflakeId
         */
        public synchronized long nextId() {
            long timestamp = timeGen();
            // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
            if (timestamp < lastTimestamp) {
                throw new RuntimeException(
                        String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
            }
            // 如果是同一时间生成的，则进行毫秒内序列
            if (lastTimestamp == timestamp) {
                sequence = (sequence + 1) & sequenceMask;
                // 毫秒内序列溢出
                if (sequence == 0) {
                    // 阻塞到下一个毫秒,获得新的时间戳
                    timestamp = tilNextMillis(lastTimestamp);
                }
            }
            // 时间戳改变，毫秒内序列重置
            else {
                sequence = 0L;
            }
            // 上次生成ID的时间截
            lastTimestamp = timestamp;
            // 移位并通过或运算拼到一起组成64位的ID
            return ((timestamp - twepoch) << timestampLeftShift)
                    | (dataCenterId << dataCenterIdShift)
                    | (workerId << workerIdShift)
                    | sequence;
        }

        /**
         * 阻塞到下一个毫秒，直到获得新的时间戳
         *
         * @param lastTimestamp 上次生成ID的时间截
         * @return 当前时间戳
         */
        private long tilNextMillis(long lastTimestamp) {
            long timestamp = timeGen();
            while (timestamp <= lastTimestamp) {
                timestamp = timeGen();
            }
            return timestamp;
        }

        private long timeGen() {
            return System.currentTimeMillis();
        }

        public long getMaxWorkerId() {
            return 63L;
        }

        public long getMaxDatacenterId() {
            return 63L;
        }

        public long getTwepoch() {
            return twepoch;
        }

        public long getWorkerIdBits() {
            return workerIdBits;
        }

        public long getDatacenterIdBits() {
            return datacenterIdBits;
        }

        public long getSequenceBits() {
            return sequenceBits;
        }

        public long getWorkerIdShift() {
            return workerIdShift;
        }

        public long getDataCenterIdShift() {
            return dataCenterIdShift;
        }

        public long getTimestampLeftShift() {
            return timestampLeftShift;
        }

        public long getSequenceMask() {
            return sequenceMask;
        }

        public long getWorkerId() {
            return workerId;
        }

        public long getDataCenterId() {
            return dataCenterId;
        }

        public long getSequence() {
            return sequence;
        }

        public long getLastTimestamp() {
            return lastTimestamp;
        }
    }

    public static void main(String[] args) {
        System.out.println(IdGenerateUtil.genId());
    }
}